code: def prepare_data(self):
      # download
      MNIST(self.data_dir, train=True, download=True)
      MNIST(self.data_dir, train=False, download=True)
  
imports: from __future__ import annotations
  import pytorch_lightning
  import torch
  import torch.nn.functional
  from torch.optim.lr_scheduler import ExponentialLR
  from torch.utils.data import random_split, DataLoader
  from torchmetrics.functional import accuracy
  from torchvision.datasets import MNIST
  from torchvision import transforms
  import nni
  from .simple_torch_model import SimpleTorchModel
label_desc: Use image node_id 2 for calling the MNISTDataModule obj's underlying member method code with example usage: obj.prepare_data() without return types